This invention relates generally to stepmotor drive, and systems utilizing stepmotor drive, and more particularly concerns controlling stepmotors of the permanent magnet type having a permanent magnet disc rotor.
Step motors are commonly used to mechanically drive devices such as the pick up heads for computer magnetic disc storage drives. A less common application of stepmotors is in actuating fluid control valves, typically having a ball or other fluid closure member, and in substantially larger horsepower ratings, furnishing rotary torque for power operated doors typically as used on mass transit vehicles such as subway cars.
Applications of the latter type are disclosed in U. S. Pat. No. 4,511,832, wherein the stepmotor drive is controlled by counting pulses applied to the stepmotor and comparing the number of pulses applied to the drive motor windings with a count of the drive motor shaft rotation in order to detect any obstruction or failure of the rotor to move.
In applications of the type contemplated by the invention disclosed herein, it is often inconvenient, difficult and expensive, or impossible to measure the stepmotor rotor movement or obtain other shaft position data at the point of application of torque load. In the case of actuating a vehicular power door, rotation of the drive motor shaft may not supply vital information relating to output shaft load requirements, in that failure of other mechanical portions of the drive system such as a fractured actuating arm or drive belt will not be reflected in the motion of the drive motor itself. Therefore, more sophisticated information regarding the shaft torque loading is necessary.
In the stepmotor operation of a rotating valve, similar failures in the mechanical drive train such as stripped gears, and/or broken gear shafts, may not be reflected in stepmotor shaft counts, rendering this type of drive system control highly unreliable, and again requiring sophisticated information as to shaft torques encountered in each operation.
Therefore it is an object of this invention to provide a stepmotor drive and control system wherein shaft load variations are monitored and analyzed in real time in order to make appropriate changes in the system drive motor actuating need.
It is a further object of this invention to provide a method of analyzing drive motor current signatures in response to applied voltage pulses wherein instantaneous information relating to output shaft loading can be compared to predetermined characteristics and limits.
It is an additional object of this invention to provide a stepmotor drive system wherein motor winding signatures are analyzed using a "SIGNALYSIS" algorithm for rapid and accurate recognition/determination of unexpected shaft loading conditions.
It is yet a further object of this invention to provide a stepmotor drive system wherein the position of the stepmotor output shaft can be obtained from predetermined or continuously varying system input data.